1. Field of the Invention
The invention relates to monoesters and a macrocyclic diester of phthalic acid and derivatives thereof. Such esters of phthalic acid and derivatives thereof are useful in the preparation of thermoplastic polymers. The thermoplastic polymers may be used to prepare coatings, inks, reinforced plastics and packaging.
2. Description of the Related Art
The synthesis of lactones, or cyclic esters, derived from either hydroxyacids or from diacids and dihydroxy compounds is well known to the art. (Carothers, W. H., Collected Papers of Wallace Hume Carothers on High Polymeric Substances, Eds. H. Mark and G. S. Whitby, Interscience Publishers, Inc., 248-259 (1940)). Examples include .delta.-valerolactone, prepared by cyclization of 5-hydroxypentanoic acid, and lactide, prepared by the dimerization of lactic acid. These simple compounds which contain six-membered lactone rings are readily prepared in good yield, as are similar lactones with five atoms in the ring, such as .gamma.-butyrolactone. Seven-membered ring lactones, such as, for example, .epsilon.-caprolactone, can also be readily prepared. However, the synthesis of lactones with larger rings, particularly those with eight to twelve ring atoms, has proven to be more difficult.
Macrocyclic di- and tetraester compounds, including cyclic esters derived from equimolar amounts of .sigma.-phthalic acid and a glycol, have been prepared. (Bradshaw et al., Chem. Revs.79:37 (1979)). However, the diesters, in particular those forming eight- to ten-membered rings, prepared from .sigma.-phthalic acid and simple glycols such as 1,2-dihydroxyethane, 1,3-dihydroxypropane, and 2-methyl-1,3-dihydroxypropane, were recovered in poor yields of less than 5%. (Ehrhart, W. A., J. Org. Chem. 33:2930 (1968)). The poor yields are believed to be due to inherent ring strain as a result of the two carbonyl groups. (Drewes et al., J. C. S. Perkin I, 2148 (1972)). The synthesis of a cyclic tetraester compound from phthalic anhydride and 1,3-dihydroxy-2,2-dimethylpropane was also achieved in very low yields of only 1.7%. (Chen et al., J. Applied Appl. Polym Sci. 41:2517 (1990)).
There still exists a need in the art for a synthetic route to prepare cyclic esters or lactones from a phthalic acid derivative and a simple glycol in high yield and purity. The cyclic esters provide unique intermediates in the production of thermoplastic polymers such as polyesters. These polyesters can be used in coatings, inks, reinforced plastics and packaging.